In the case of thermal machines, in particular gas turbines, there are various components that on the one hand have corners and edges as a result of their structural design and on the other hand are exposed to high thermal loading at these places during operation. An example of such a component is a moving blade of a gas turbine, made up of multiple parts, such as that disclosed for example in the document EP 2 189 626 A1. FIGS. 1 and 2 of this document are reproduced as FIG. 1 in the present application.
The parts shown in FIGS. 1A and 1B, a platform element 10 and a blade airfoil element 20, are assembled and connected to one another to form a moving blade. The platform element 10 has in the upper side 11 a through-opening 12, through which the blade airfoil element 20 can be fitted with the blade airfoil 17, ending in a blade tip 18. Serving for securing the assembled blade are legs 13, 14 with formed-on hooks 15, 16 on the underside of the platform element 10 and a blade root 21 on the blade airfoil element 20, which is connected to the blade airfoil 17 by way of a shaft 19.
In the assembled state, there is a transition between the blade airfoil 17 and the upper side 11 of the platform element 10, which is shown enlarged and in section in FIG. 2. A gap 23, which is formed between the parts 17 and 11 and is subjected to the hot gas flowing around the blade airfoil 17, produces an edge 22 with a corner region 24, which is subjected to high thermal loading.
Until now, this edge 22 (running perpendicularly to the plane of the drawing in FIG. 2) has been cooled by a cast cooling channel being provided parallel to the edge 22. However, such a cooling channel is not very efficient, because                a) with a cast channel, the distance from the surface is comparatively great, which leads to higher temperatures in the corner region 24; and        b) with a cast channel, the inside diameter is comparatively great, which leads to a higher consumption of cooling air.        
For this reason, oxidation and crack formation occur to a not inconsiderable extent at the edge 22 because of inadequate cooling.
To solve this problem, it has already been proposed (see the document JP 2010144656 or U.S. Pat. No. 7,597,536 B1) to reduce the extent to which the edge is subjected to hot gas by for example providing flushing with cooling air. The disadvantage of this is that a considerable amount of flushing air is required to keep down the temperature of the mixed hot gas. In particular in the case of relatively large gaps, the required amount of flushing air increases significantly. If the gap width changes during operation in a way that does not correspond to the desired amount of flushing air, this type of cooling becomes ineffective. In the worst case, the flushing air may flow directly into the main stream, if the flow conditions change during operation. For these reasons, the gap is left largely without cooling, because both solution proposals presuppose a balanced mixture of hot gas penetrating into the gap and flushing air supplied through bores.